Physicians now enjoy a moment of tactical advantage in the evolution of the struggle for control over health care in the United States. The most effective way to capitalize on this-perhaps fleeting-position and to more permanently alter the balance of power in their favor is for physicians to establish strong and visionary leadership in health care quality improvement. Such an undertaking, if successful, could place the very essence of health care-defining, measuring, and improving its quality-in the hands of physicians. To succeed requires understanding the relationships between the different kinds of quality problems that plague our health care system, the various kinds of errors that lead to them, and how amenable these different kinds of errors may be to different interventions. The authors delineate a conceptual framework that describes these relationships, as well as their implications for conducting effective and durable quality improvement. The authors then illustrate how physicians could engage in this activity in three different settings: a four-or-five-physician primary care practice, a 50-physician multispecialty group, and a 450-bed community hospital. Finally, the authors submit that now is an opportune time for physicians and the organizations they direct or guide to take the leadership role in conducting health care quality improvement. Realizing the opportunity will require dedicating significant resources and changing traditional approaches to quality, but in so doing, physicians can regain much of the autonomy over the practice of medicine previously lost to government and managed care.